BP-33: Move releasing official docker images out of main repo

Motivation

Current bookkeeper docker images are auto-built by apache docker account. However it becomes problematic in the release process:

Docker autobuild uses release tag for labeling the versions for docker images. But the Dockerfile can only be updated after
a release is successfully made. So we have to retag a release after a release, in order to update Dockerfile to build the docker
image.

Proposed Changes

Follow what flink is doing, and maintain the docker files outside of the bookkeeper main repo.

Create an organization asfbookkeeper-ecosystem for hosting repos that related bookkeeper but not necessarily needed to be put in main repo.

Create a repo docker-bookkeeper under asfbookkeeper-ecosystem for hosting the docker files following the suggested practices from making a docker official image.

Add a library definition file under docker-library/official-images for bookkeeper.

Add an image doc under docker-library/docs for bookkeeper.

Update the release guide on how to update docker images at the end of each release.

Remove docker dir from main repo or make it used for building unreleased docker images only.